#menu {
    width:200px;
    /*border:1px solid red;*/
}
#menu ul {
    list-style: none;
    padding: 0px;
    margin: 0px;
}
#menu ul li {
    border-bottom: 1px solid #fff;

}
#menu ul li a {
    /*先将a标签转换为块级元素，才能设置宽和内间距*/
    display: block;
    background-color: #00a6ac;
    color: #fff;
    padding: 5px;
    text-decoration: none;
}
#menu ul li a:hover {
    background-color: #008792;
}